A capacitor discharge type breakerless ignition system is well known which comprises a capacitor to charge an electric energy and a controlled semiconductor switching device to control the discharge of the electric energy through a primary coil of an ignition coil whereby a secondary coil of the ignition coil has a high voltage established thereacross. For this type of the ignition system is required a controlling signal applied to the semiconductor switching device in time with the operation of an engine and yet the signal is required to conduct the device in an advanced phase in accordance with the revolution number of the engine.
In general, a signal generator has been widely used which comprises a magnet rotor rotating in synchronism with the internal combustion engine and a stator fixed relative to the rotor to generate a signal. One of the prior signal generators has the stator provided with a plurality of coils wound around teeth of a comb-like magnetic core, and designed to induce a plurality of signals different in the amplitude from each other, respectively. Only one half wave portions of the signals from the respective coils have been picked up and combined with each other. The coils have been arranged so that the coil in the most retarded position induces the signal of the largest amplitude and the coil in the most advanced position induces the signal of the smallest amplitude. Combination of the signals from the respective coils have been effected through respective diodes connected in series to the corresponding coils. During relatively low number of revolution of the engine, the signal from the coil in the most retarded position reaches the gate-on level of the semiconductor switching device, resulting in conduction of the device in most retarded phase. During relatively high number of revolution of the engine, the signal from the coil in the most advanced position reaches the gate-on level of the semiconductor switching device, resulting in conduction of it in most advanced phase. The disadvantage of the prior art is that indivisual diodes have been required for the respective coils. As a result, the required number of the diodes increases as the number of the coils increases, which makes the ignition system expensive.